Field optimisation in a synchronous generator with high temperature superconducting field winding and magnetic core

A series of 2-D and 3-D modelling investigations are used to evaluate and optimise the field distribution of the hybrid salient pole rotor of a 100 kVA high temperature superconducting synchronous generator. The salient pole rotor core is formed from a stack of 9% nickel steel plates, which are tied together using through bolts. A series of 2-D models was used to optimise the field distribution of the machine with no bolts in the rotor. Then a 3-D model was constructed with the bolts included. The differences between the predictions of the 2-D and 3-D models were evaluated, and the flux distortion caused by the bolts and their holes was estimated. A simple formula was devised to guide the designer in improving the voltage waveform. Changes to the shape of the rotor were proposed and the 3-D model was modified to confirm the effectiveness of these changes in reducing the undesirable harmonics.